The field of the invention relates generally to gas turbine engines, and more particularly, to a system and method for cleaning receiver slots after stator ring segments or singlet blades have been removed from a turbine engine.
At least some known gas turbine engines include, in serial flow arrangement, a high-pressure compressor for compressing air flowing through the engine, a combustor wherein fuel is mixed with the compressed air and ignited to form a high temperature gas stream, and a high pressure turbine. Hot combustion gases are channeled downstream from the combustor towards the turbine, wherein energy is extracted from the combustion gases for use in powering the compressor, as well as producing useful work to propel an aircraft in flight or to power a load, such as in an electrical generator. Some known gas turbine engines may also include a low-pressure compressor, or booster compressor, to supply compressed air to the high pressure compressor.
Known compressors include a compressor casing that may include upper and lower casing sections that are coupled about a rotor assembly. Known compressors include a plurality of alternating rows of circumferentially-spaced stator and rotor blades. Each row of rotor and stator blades includes a series of airfoils that each include a pressure side and a suction side that are coupled together at leading and trailing edges. Each stator blade airfoil extends radially inward from a stator support ring that is inserted into channels (receiver slots) that are circumferentially formed in axial succession within a radially-inner side of the combustor casing. Each stator ring segment is sized and shaped to receive a plurality of stator blade segments that extend circumferentially in a row between a pair of adjacent rows of rotor blade assemblies. Alternatively for some stages of a gas turbine compressor, a root of a platform for singlet blades may directly inserted into the channels (receiver slots) of the casing without the need for an intervening stator ring segment.
During operation, leading and trailing edges and/or an outer tip of the stator blade may deteriorate or become damaged due to oxidation, thermal fatigue cracking, or erosion caused by abrasives and corrosives in the flowing gas stream. Over time such deterioration may cause some known stator blades to fail, resulting in the airfoil portion becoming detached from a dovetail portion of the blade. In some instances, blade failures have caused catastrophic damage within their engine. To facilitate mitigating such operational effects, blades are periodically inspected for damage, to enable a determination of an amount of damage and/or deterioration to be made. Blades are generally replaced if the damage and or deterioration meets a certain pre-determined threshold. Alternatively, if the blades have not lost a substantial quantity of material, the blades may be repaired.
For example, at least one known method of replacing stator ring segments requires the removal of the upper compressor section casing and rotor assemblies. Following rotor assembly removal, each stator blade segment is heated and after reaching a desired temperature, the segment is quenched to facilitate rapid cooling. Each segment is then withdrawn from its respective channel using, for example, a pneumatic peening hammer. A newly fabricated segment is then inserted into the casing channel. Alternatively, after being removed from the rotor assembly, each damaged or deteriorated segment is repaired and refurbished prior to being replaced within the casing channel. However, rotor assembly removal, reinsertion, and compressor reassembly may be a time-consuming and expensive process that may significantly increase repair time and power generator outages. Such concerns are similarly applicable to the removal of singlet blades inserted directly into the receiver slots.
Methods and systems have been proposed, for example by Corn et al. (U.S. Ser. No. 12/110,729 filed Apr. 28, 2008), for removal of stator ring segments without removal of the rotor. After the removal of the stator blades (including segmented stators) in the axial compressor portion of a gas turbine, the receiver slots and hook-fits must be cleaned to receive the new stators (stator ring segment or singlet blade). If not cleaned properly, the new stator(s) may become bound or locked up while re-installing stators before achieving the final assembly position, thereby causing irreversible damage to the stator components and/or may create the need to remove the rotor as a means to mitigate bound stators, which significantly increases cost for the operation.
Because the rotor is closely fitted to the mid-compressor case, it is geometrically difficult to reach the areas that must be cleaned. Additionally, the use of grinders utilizing aluminum oxide wheels create residual dust and foreign object damage that is not desired within the axial compressor gas path. Moreover, the extended reach necessary to access the areas to be cleaned underneath the rotor and rotor blades creates an ergonomic issue potentially leading to operator injury.
A current process to clean receiver slots and hook-fits prior to stator re-installation utilizes a ninety-degree pneumatic grinder, fitted with aluminum oxide grinding discs, and/or other light abrasive wheels as a means to clean trash, oil, rust/oxidation, and other foreign materials from receiver slots and hook-fits to clear the path for the new stators. The desired process for stator removal requires the rotor to remain in place making access to the areas to be cleaned difficult. The dust and grit remaining in the unit after cleaning inherently related to the cleaning process can also cause binding of the new stators during installation and is not a desired condition in the gas path of the axial compressor.
Accordingly, there is a need for a method to clean the receiver slots and hook-fits for removed stators of trash, oil, rust/oxidation, and other foreign materials so as to provide a clear insertion path for the new stators. The cleaning method should be performed while the rotor remains in place and should not damage the receiver slots.